The present invention relates to methods for controlling a hydraulic brushless motor and controlling devices, and more specifically, relates to a method and a device for controlling the brushless motor mounted on an automobile and used in hydraulic pumps and the like.
A DC motor with brush is conventionally used as an electrically operated motor for driving the hydraulic pump for transmission or power steering mounted on the automobile, but problem regarding reliability due to durability of the brush arises. The brushless motor is thus desirably used.
The controlling device of the brushless motor is configured by a motor with magnetic coils of three phases, the U phase, the V phase and the W phase; and a switching circuit including six switching elements for driving the motor.
The operation of the brushless motor is performed by sequentially switching the switching element for conduction to the magnetic coils of three phases. For example, if the conduction angle is 60 degrees, the conduction signal of each switching element is continuously turned ON only over 120 degrees out of the electrical angle of 360 degrees, whereby the conduction of 120 degrees is performed in each switching element. Two out of six switching elements are simultaneously turned ON, where one of the two switching elements that are turned ON is turned OFF and one of the other four switching elements is turned ON every 60 degrees. This operation is subsequently repeated. The method for controlling the motor for operating the motor by sequentially switching each switching element in the above manner is known. In the motor of the in-vehicle hydraulic pump, high torque low rotation is required when the oil temperature is low, and low torque high rotation is required when the oil temperature is high.
Since the usage voltage is relatively low and restrictions such as current consumption and size are extremely severe for the in-vehicle motor, the required output is particularly difficult to obtain on the high torque side, and the required output points for both the high oil temperature and the low oil temperature cannot be satisfied without enlarging the motor when the method for controlling the motor by 60 degrees conduction as disclosed in patent article 1 is applied (see patent article 1=Japanese Laid-Open Patent Publication No. 05-103454)